A storage system is a computer that provides storage service relating to the organization of information on storage devices, such as disks. The storage system may be deployed within a network attached storage (NAS) environment and, as such, may be embodied as a file server. The file server or filer includes a storage operating system that implements a file system to logically organize the information as a hierarchical structure of directories and files on the disks. Each “on-disk” file may be implemented as a set of data structures, e.g., disk blocks, configured to store information. A directory, on the other hand, may be implemented as a specially formatted file in which information about other files and directories are stored.
The filer may be further configured to operate according to a client/server model of information delivery to thereby allow many clients to access files stored on a server, e.g., the filer. In this model, the client may comprise an application, such as a database application, executing on a computer that “connects” to the filer over a computer network, such as a point-to-point link, shared local area network (LAN), wide area network (WAN), or virtual private network (VPN) implemented over a public network such as the Internet. Each client may request the services of the file system on the filer by issuing file system protocol messages (in the form of packets) to the filer over the network.
A common type of file system is a “write in-place” file system, an example of which is the conventional Berkeley fast file system. In a write in-place file system, the locations of the data structures, such as inodes and data blocks, on disk are typically fixed. An inode is a data structure used to store information, such as meta-data, about a file, whereas the data blocks are structures used to store the actual data for the file. The information contained in an inode may include, e.g., ownership of the file, access permission for the file, size of the file, file type and references to locations on disk of the data blocks for the file. The references to the locations of the file data are provided by pointers, which may further reference indirect blocks that, in turn, reference the data blocks, depending upon the quantity of data in the file. Changes to the inodes and data blocks are made “in-place” in accordance with the write in-place file system. If an update to a file extends the quantity of data for the file, an additional data block is allocated and the appropriate inode is updated to reference that data block.
Another type of file system is a write-anywhere file system that does not overwrite data on disks. If a data block on disk is retrieved (read) from disk into memory and “dirtied” with new data, the data is stored (written) to a new location on disk to thereby optimize write performance. A write-anywhere file system may initially assume an optimal layout such that the data is substantially contiguously arranged on disks. The optimal disk layout results in efficient access operations, particularly for sequential read operations, directed to the disks. A particular example of a write-anywhere file system that is configured to operate on a filer is the SpinFS file system available from Network Appliance, Inc. of Sunnyvale, Calif. The SpinFS file system is implemented within a storage operating system having a protocol stack and associated disk storage.
Disk storage is typically implemented as one or more storage “volumes” that comprise physical storage disks, defining an overall logical arrangement of storage space. Currently available filer implementations can serve a large number of discrete volumes (150 or more, for example). Each volume is associated with its own file system and, for purposes hereof, volume and file system shall generally be used synonymously. The disks within a volume are typically organized as one or more groups of Redundant Array of Independent (or Inexpensive) Disks (RAID). RAID implementations enhance the reliability/integrity of data storage through the redundant writing of data “stripes” across a given number of physical disks in the RAID group, and the appropriate caching of parity information with respect to the striped data. As described herein, a volume typically comprises at least one data disk and one associated parity disk (or possibly data/parity partitions in a single disk) arranged according to a RAID 4, or equivalent high-reliability, implementation.
It is advantageous for the services and data provided by a filer or storage system to be available for access to the greatest degree possible. Accordingly, some storage system environments provide a plurality of storage systems (i.e. nodes) in a cluster where data access request processing may be distributed among the various nodes of the cluster. Distributed processing in the cluster is enabled, in part, by a unified namespace presented to clients. As used herein, the term “unified namespace” denotes that any volume may be presented and served by any node of the cluster even if the volume is not directly connected to the node. The cluster configuration ensures that each request is forwarded to the appropriate node that services a particular file system (or volume) for processing.
In addition, a collection of management processes executes on each node to provide cluster configuration (i.e., management data) for the nodes. Each of these processes has interfaces to a replicated database (RDB) that provides a persistent object store for the management data. The RDB replicates and synchronizes changes (updates) made to the management data by the management processes across all nodes of the cluster. The use of a unified namespace in combination with cluster configuration thus provides ease of management for an administrator of the cluster.
A noted disadvantage related to the unified namespace of a cluster arises when performing certain backup operations using a network management protocol, such as the Network Data Management Protocol (NDMP) defined in Network Data Management Protocol Version 4, dated April 2003, the contents of which are hereby incorporated by reference. In a network management protocol environment, a backup manager executing backup software transmits data access requests to the cluster to perform, e.g., desired backup/restore operations. As a result of the unified namespace feature, described above, these requests may be directed to any one of a plurality of nodes within the cluster for servicing.
When using a backup/restore protocol such as NDMP, a request directed to initiate a backup operation of a particular volume typically returns an error if the volume is not local (i.e., not directly connected) to the node receiving the request. Use of the NDMP protocol in a unified namespace cluster is further problematic when volumes are relocated from node to node for failover and/or load balancing purposes. The resulting errors that occur because the volumes are no longer local to the nodes receiving the backup operations present a disadvantage to the administrator, which must then track the physical locations of the volumes to ensure proper performance of the operations.
A solution to the above problem may require that the administrator update the configuration of the backup manager with the new location of each volume. However, the backup manager may “view” the relocated volume as a new volume, resulting in a next backup operation being treated as an original baseline backup operation, i.e., an entire volume “backup”, instead of only an incremental backup. This, in turn, results in wasted storage space and an increase of bandwidth and resources, as well as an unnecessary baseline backup operation.